OK so it's taken me a while to confirm this since the number of 1920Xs in my circle are limited (most went for the 1950X) and the number of 1920Xs that have tried a P-State OC...however I can confirm that there is something wrong with BIOS or AGESA that means 1920X P-State OC does not work whereas 1950X does. Someone at AMD needs to take a look at this!